What Iyorvin said - I was a drow was well. Pump unholy as far as it will go, dual malforms+charmie for pure offense (with malform changes one malform and one good weapon first). Dirt;flee and return, use your damage spells when you can't lag, curse if they keep recalling on you. I think the only time I cast plauge/poison was on cleaved to sleep players after I summoned them. It happened twice in ~100 kills.
Hunt, hunt, hunt, hunt. When you're not hunting, you're sitting in your bolt hole hiding. Don't let other players attack you until you are fully pumped and after them. DKs are a purely offense class.
L-A